Process for extraction of glucosinolates from broccoli seeds

ABSTRACT

A new process for extracting and purifying glucosinolates from plant material, preferably broccoli sprouts or seeds is described. An alcoholic extract is adsorbed onto a basic resin and eluted with ammonia. Optionally, the alcoholic extract is passed through an ion-exchange column containing acidic resin prior to the adsorption/elution step.

BRIEF DESCRIPTION OF THE INVENTION

This invention relates to a process for extracting glucosinolates frombroccoli seeds, sprouts, or florets which comprises a step of adsorbinga broccoli seed extract on a basic resin, followed by elution of theadsorbed glucosinolates and collecting the glucosinolate-rich eluate.

BACKGROUND OF THE INVENTION

Broccoli seeds have a high amount of glucosinolates, includingglucoraphanin, glucoiberin, glucoerucin. While the glucosinolates arenot biologically active, cleavage by the enzyme myrosinase (present inmany plant cells and in the gut microflora) results in the formation ofactive isothiocyanates. These isothiocyanates, including sulforaphane,have been shown to have numerous health-promoting properties, and insome experiments have even been shown to exert various anti-cancereffects.

Previously, various authors have developed extraction/purificationschemes to obtain glucoraphanin from broccoli seeds. For example, Westet al. 2002 J. Chromatog A 966:227-232 describes use of ion-pair andhydrophilic interaction chromatographies for purifying variousglucosinolates. See also Toribio et al. 2007 J. Chromatog A 1170:44-51which describes purification of sinalbin and glucoraphanin using strongion-exchange displacement centrifugal partition chromatography. However,both these techniques are directed to purification of compounds, and notmerely extracting a glucoraphanin-containing extract from broccoli seedswhich is economical and uses food-grade reagents.

It would be desirable to have a simple, robust glucosinolate extractionmethod which is suitable for production of food-grade ornutraceutical-grade glucosinolates, especially glucoraphanin.

DETAILED DESCRIPTION ON THE INVENTION

A new process for the production of a glucosinolate-containing extracthas been developed in accordance with this invention, which comprisesthe steps of

-   -   a) extracting glucosinolate-containing plant parts or seeds, or        an extract of glucosinolate-containing plant parts or seeds with        an extraction medium that comprises a lower alcohol or ketone or        an aqueous mixture of a lower alcohol or ketone to obtain a        alcoholic or ketonic extract;    -   b) optionally completely or partially evaporating the extraction        medium of step a);    -   c) optionally contacting the extract of step a) or step b) with        a cation exchange resin;    -   d) adsorbing the extract from step a), step b), or step c) onto        a basic resin; and    -   e) optionally eluting the resulting glucosinolate-containing        extract.

Suitable solvents for step b) through e) include water, C1-4 alcohols,C3-4 ketones, and mixtures thereof.

The cation exchange resin is preferably in its acidic form, and morepreferably a strong acidic ion exchanger is used.

If desired, an additional step may be performed on theglucosinolate-containing extract obtained from step e). In thisembodiment of the invention, the volatiles of theglucosinolate-containing extract are evaporated. The result of this stepis a solid extract containing glucosinolates, which includesglucoraphanin, glucerucin, and glucoiberin. The solid extract made bythis process also forms another aspect of this invention.

The starting materials for this invention may be anyglucosinolate-containing plant material, or any glucosinolate-containingextract. Preferably, the plant material is from the Brassicaceae family,such as broccoli, mustard, rapeseed, cauliflower, kohlrabi, cabbage, bokchoy, turnip, radish, wasabi, horse radish and brussel sprouts.

The plant parts may be the sprouts or seeds, as it is known that sproutsand seeds often contain higher amounts of glucosinolates than matureplant leaves, but florets or heads may also be used. If desired, theplant parts may be first subjected to a pre-treatment step of washing,or de-fatting (for seeds). In preferred embodiments, the plant is abroccoli plant, and seeds are extracted. In this case, the originalstarting material for the process may be either a broccoli seed extractor the broccoli seeds themselves.

If one starts with plant parts, optionally washed and/or defatted and/orotherwise treated, then they are subjected to an extraction step. Inthis extraction, it is preferable to use an aqueous medium, or a loweralcohol or ketone wherein a lower alcohol or ketone is a C1 to C4alcohol or ketone or mixtures thereof. This may be performed in thepresence of charcoal or other similar material such as celite. See, forexample Toribio et al., supra. The extract obtained can then be used inthe next step. If desired, the extract can be subjected to furtherpurification steps such as ultrafiltration. Also the extract may beoptionally concentrated by a complete or partial evaporation of thesolvent.

In the next step, the extract of plant parts (either as obtained above,or, optionally, a commercially available extract) is then extracted withan extraction medium which comprises a lower alcohol or lower ketone.The term “lower alcohol” or “lower ketone” means that the alcohol is aC1-C4 alcohol or the ketone is a C3-C4 ketone, or mixtures thereof; andis preferably an alcohol or ketone which is approved for use in foodmanufacturing, such as ethanol or acetone, although using technicalethanol may also be used. The alcohol or ketone are preferably ethanolor acetone, and may be in an aqueous solution such as at least about 40%alcohol or ketone; in a preferred embodiment, the lower alcohol or lowerketone is at least about 70% in an aqueous solution, and in a morepreferred embodiment it is from about 70% to about 95%. In this step,temperature is not particularly critical. The extract may be filtered ordecanted to separate the solubles from the insolubles.

The extract may be evaporated to remove the volatiles, followed bydissolving in an appropriate solvent such as water, lower alcohols,ketones, or a mixture thereof for the next step.

Optionally, the alcoholic or ketonic extract in the appropriate solventor solvent mixture is subjected to a cationic ion-exchange column,preferably a strong acidic resin, in its acidic form such as DOWEX® 50Wor AMBERLYST® 15 (both available from Sigma Aldrich). It is alsopreferred, in keeping with the intended use of the final product as anutraceutical or food ingredient, that the resin is chosen as to meetregulatory requirements for food production.

The extract which is obtained from either the alcoholic extraction step,or preferably the ion-exchange step, is then adsorbed onto a basicresin. The basic resin may be either a strongly or weakly basic resin,preferably a weakly basic resin. Examples of suitable resins includeAMBERLITE® IRA-67, and LEWATIT® VPOC 1065, (both available from SigmaAldrich). In keeping with the goal of manufacturing nutraceutical/foodgrade material, it is preferred that the resin be suitable from aregulatory view for this purpose. For this step, temperature is notparticularly critical; ambient temperature is preferred.

The ion-exchange column so-prepared is then eluted with a base such asammonia, diluted potassium hydroxide, sodium hydroxide, sodiumcarbonate, sodium hydrogen carbonate or the like, in water, loweralcohol (C1-C4) or acetone or in mixtures thereof. The preferred base isammonia in water, lower alcohol (C1-C4) or mixtures of the solvents.

The resulting eluate (final extract) contains glucosinolates in a morepurified form than the original starting material. While actual amountsof major products may vary from lot-to-lot, depending on the content ofthe starting plant material; a typical final extract will contain thefollowing major glucosinolates: glucoraphanin, glucoerucin, andglucoiberin. This product forms yet another embodiment of thisinvention.

If desired, the final extract may be evaporated, freeze-dried orspray-dried using conventional means so that it is a solid extract.These processed solid extracts also form an aspect of this invention.

In one preferred embodiment of the invention, the extract after ionexchange treatment and elution with ammonia, contains the ammonium saltof glucoraphanin as a major product. In an optional, but preferred step,the ammonium salt is changed into an ammonium-free extract suitable forfurther processing. In this optional step, the extract which is acidic,is made more basic. This can be done by adding any conventional sourceof base, such as alkali- or earth alkali hydroxides, such as magnesiumhydroxide, calcium hydroxide, sodium hydroxide, potassium hydroxide.Preferably the base is suitable for use in food, such as sodiumhydroxide.

Enough base is added so that the pH rises to above 7.0, more preferablyto about pH 7 to pH 12, and even more preferably to pH 9 to 11.

The addition of a base such as sodium hydroxide to form a basicenvironment, such as from pH 9 to 11, allows the exchange of ammoniumions to sodium ions. The volatiles can then be separated from theresulting sodium glucosinolate by conventional means, such as by use ofreduced pressure (i.e. removed using a partial vacuum), resultingan-ammonium free extract.

The following non-limiting Examples better illustrate the invention

Example 1

An extraction was made following the procedure generally described in A.Toribio et al.; J. Chromatogr. A 1170 (2007) 44-51, which is herebyincorporated by reference. 3 kg of broccoli seeds were stirred for 2 hin 20 liters of water at reflux temperature. The resulting warm solutionwas filtered. The filtrate was then agitated for 2 h with 150 g ofcharcoal. The suspension was filtered and concentrated at reducedpressure at 60° C. to 310 g residue with a glucoraphanin content of 12%.

Example 2

4.0 g of the residue of Example 1 was suspended in 40 ml of anethanol:water (82%:18%) mixture and heated to reflux for approximately30 min. The resulting suspension was filtered and the mother liquid wasevaporated under reduced pressure (30 mbar) at 60° C. An extract wasobtained (2.2 g) with a purity of glucoraphanin of 16%.

Example 3

2 g ion exchanger AMBERLITE® IRA-67 was stirred with 2.0 g extract ofExample 1 in 10 ml water for 30 min. The liquid was removed byfiltration and the loaded ion exchanger washed with water (5 ml). Theloaded ion exchanger was stirred at ambient with 10 ml 5% aqueousammonium hydroxide solution in methanol for 30 min. After filtration,the filtrate was evaporated under reduced pressure (30 mbar, 70° C.).

The result was 97.3 mg of extract containing glucoraphanin with a purityof 54%

Example 4

Washing the loaded ion exchanger of Example 3 with 10 ml 5% aqueousammonium hydroxide solution in water yielded, after evaporation 217 mgglucoraphanin with a purity of 19%.

Example 5

2 g acidic ion exchanger AMBERLYST® 15 was stirred with 1 g extract ofExample 2 in 10 ml water for 30 min at ambient temperature. The liquidwas removed by filtration and the ion exchanger washed with water (5ml). The eluate, containing the free glucoraphanin acid, was stirredwith the weakly basic ion exchanger AMBERLYST® IRA-67 (2 g) for 30 min.at ambient temperature. The liquid was removed by filtration and theloaded ion exchanger washed with water (10 ml). The loaded ion exchangerwas stirred with 10 ml of a solution of 5% aqueous ammonia in methanolfor 30 min at ambient. After filtration, the eluate was evaporated underreduced pressure (30 mbar, 70° C.). Yield: 95.2 mg glucoraphanin with apurity of 69% (determined by HPLC).

Example 6

Washing the loaded basic ion exchanger from Example 5 with 5% aqueousammonium hydroxide solution in water yielded after evaporation, 385.3 mgglucoraphanin (purity 25%).

Example 7

1 g of the extract of Example 5 was stirred in 10 ml water. An aqueoussolution of sodium hydroxide (1 N) was added until a pH of 10.5 wasreached. The mixture was stirred for 30 min at room temperature and thevolatiles were removed under reduced pressure (30 mbar, 70° C.). Yield:980 mg glucoraphanin with a purity of 64% (determined by HPLC). 42% ofthe ammonium ions were exchanged to sodium ions.

1. A process for obtaining a glucosinolate-containing extract fromglucosinolate-containing plant parts or seeds or from an extract ofglucosinolate-containing plant parts or seeds comprising the steps of:a) extracting the glucosinolate-containing plant parts or seeds, or theextract of glucosinolate-containing plant parts or seeds with anextraction medium that comprises a lower alcohol or ketone or a mixturethereof with water, to obtain a alcoholic or ketonicglucosinolate-containing extract; and b) optionally contacting theglucosinolate-containing extract of step a) with a cation ion-exchangeresin; and c) adsorbing the glucosinolate-containing extract from eitherstep a) or step b) onto a basic resin; and d) optionally eluting theresulting glucosinolate-containing extract.
 2. A process according toclaim 1, further comprising evaporating the volatiles from resultingglucosinolate-containing extract.
 3. A process according to claim 1,wherein the cation exchange resin of step b) is a strongly acidic resin.4. A process according to claim 1, wherein the alcohol of step a) is aC1-C4 alcohol.
 5. A process according to claim 4 wherein the alcohol isethanol.
 6. A process according to claim 1, wherein the ketone of stepa) is acetone.
 7. A process according to claim 4, wherein the C1-C4alcohol or acetone is present in an aqueous solution at a concentrationof at least about 40%.
 8. A process according to claim 5 wherein ethanolis present in an aqueous solution at about 70% to about 95%.
 9. Theprocess according to claim 1, where the starting material is an extractof glucosinolate-containing plant parts or seeds.
 10. The process ofclaim 1, wherein the plant parts or seeds are selected from the groupconsisting of broccoli, mustard, rapeseed, cauliflower, kohlrabi,cabbage, bok choy, turnip, radish, wasabi, horse radish and brusselsprouts.
 11. The process according to claim 10 wherein the plant isbroccoli.
 12. The process according to claim 10 wherein the plant partor seeds is broccoli seeds.
 13. The process of claim 1, furtherincluding a step of evaporation, freeze-drying, or spray-drying.
 14. Aprocess according to claim 1, further comprising adding sufficient baseto the eluate of step d), to increase the pH to at least 7.0, andseparating the resulting glucosinolate-containing salts.
 15. A processaccording to claim 14 wherein the glucosinolate-containing salts havealkali- or earth alkali cations.
 16. A process according to claim 14,wherein the separating comprises removing volatiles under reducedpressure.
 17. The product produced by the process of claim 1.